U.S. patent number 8,024,979 [Application Number 12/426,729] was granted by the patent office on 2011-09-27 for indicating fastener loading.
Invention is credited to Ronald C. Clarke.
United States Patent |
8,024,979 |
Clarke |
September 27, 2011 |
Indicating fastener loading
Abstract
An amplified indication of the elongation of a fastener is
provided for determining instantaneous loading conditions of a
fastener. A load indicator is couplable to a fastener for
instantaneous load measurement and includes a housing defining a
fastener interface configured to removably couple the housing to a
fastener. A moveable datum probe extends from the housing in
contact with a datum rod anchored within an internal bore of the
fastener. A first lever is pivotally mounted within the housing and
is moveable in response to displacement of the datum probe. A load
display indicates a degree of loading of a fastener as a function
of displacement of the datum probe. A second lever can be used to
further amplify the reading from the displacement of the datum
probe. An inclined visual scale and a multi-faceted lens allows for
viewing of loading values from multiple directions or angles.
Inventors: |
Clarke; Ronald C. (Phoenix,
AZ) |
Family
ID: |
43011448 |
Appl.
No.: |
12/426,729 |
Filed: |
April 20, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090301383 A1 |
Dec 10, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11467011 |
Aug 24, 2006 |
7520174 |
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Current U.S.
Class: |
73/761;
73/760 |
Current CPC
Class: |
F16B
31/025 (20130101); G01L 5/24 (20130101) |
Current International
Class: |
F16B
31/02 (20060101) |
Field of
Search: |
;73/760-761 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Noori; Max
Attorney, Agent or Firm: Zagorin O'Brien Graham LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. application Ser.
No. 11/467,011 filed on Aug. 24, 2006, which is incorporated herein
by reference in its entirety.
Claims
What is claimed is:
1. In combination, a fastener and load indicator for measuring an
axial tensile load on the fastener, the combination comprising: a
fastener including a head defining a reference surface and a load
indicator interface, and a shank defining, with the head, a central
bore; a datum rod having a first end anchored within the central
bore and extending along the central bore to a second free end
positioned adjacent the reference surface of the fastener head; a
load indicator housing comprising a fastener interface configured
to releasably couple the load indicator to the load indicator
interface on the head of the fastener, such that the load indicator
is substantially positioned outside the central bore; a datum probe
extending from the housing and configured to be displaced by the
datum rod as the load indicator is coupled to the fastener via the
fastener interface; a first lever having first and second ends and
being pivotally coupled to the load indicator housing and moveable
in response to displacement of the datum probe; and a load display
retained by the housing is responsive to movement of the lever to
indicate the loading of the fastener as a function of the
displacement of the datum rod, datum probe and first lever.
2. The combination of claim 1, further comprising a second lever
pivotally connected within the housing and cooperating with the
first lever and wherein the load display is responsive to combined
movement of the first and second levers.
3. The combination of claim 2, wherein an end of the second lever
is a pointer movable along a visual scale.
4. The combination of claim 3, further comprising a spring biasing
the pointer towards one end of the visual scale.
5. The combination of claim 1, wherein the load display comprises a
pointer movable along a visual scale.
6. The combination of claim 1, further comprising a multi-faceted
lens in the housing configured to allow viewing of the load display
from multiple substantially orthogonal views.
7. The combination of claim 6, wherein the visual scale is
multifaceted or inclined.
8. The combination of claim 1, wherein the load display is at least
one of an electrical signal, an audible signal and a light
signal.
9. The combination of claim 1, wherein the interfaces couple the
indicator to the fastener via at least one of a snap fit,
interference fit, threaded fit, and magnetic attraction.
10. The combination of claim 1, wherein the interfaces are
configured to align the datum probe with the free end of the datum
rod.
11. The combination of claim 1, wherein a first end of the first
lever serves as the datum probe.
12. The combination of claim 1, wherein the second end of the first
lever serves as a moveable pointer.
13. A load indicator removably couplable to a fastener for
instantaneous load measurement, the indicator comprising: a housing
defining a fastener interface configured to removably couple the
housing atop a fastener; a moveable datum probe extending from the
housing, the fastener interface configured to align the housing on
the fastener head with the datum probe in contact with a datum rod
of a fastener in use; a displacement gauge disposed within the
housing and moveable in response to displacement of the datum
probe; and a load display configured to indicate a degree of
loading of a fastener as a function of displacement of the datum
probe.
14. The indicator of claim 13, wherein the load display comprises a
visual scale and a pointer associated with the displacement
gauge.
15. The indicator of claim 14, wherein the displacement gauge
comprises a first lever and wherein a first end of the lever is the
pointer and a second end of the lever is the datum probe.
16. The indicator of claim 13, wherein the displacement gauge
comprises a first lever configured to produce a first amplified
response to movement of the datum probe.
17. The indicator of claim 16, further comprising a second lever
associated with the first lever to produce a second amplified
response to movement of the datum probe.
18. The indicator of claim 16, further comprising a spring biasing
the first lever towards one end of the visual scale.
19. The indicator of claim 13, wherein the fastener interface is
configured to attach to a complimentary feature on the fastener by
at least one of a snap-fit, interference fit, threaded connection
and magnetic attraction.
20. The indicator of claim 13, further configured to maintain a
measured load value on the load display after removal of the
indicator from a fastener.
21. The indicator of claim 13, wherein the load display includes
one of an audible signal generator and a light generator.
22. The indicator of claim 13, wherein the datum probe is a ball
bearing displaceable within a journal and contacting the
displacement gauge.
Description
FIELD OF INVENTION
This invention generally relates to load indicating, and more
particularly, to visually representing and reading loading of
fasteners and fastenings.
BACKGROUND OF THE INVENTION
Fasteners are used in a wide variety of applications, such as
mills, motors, railroad tracks, flange assemblies, petrochemical
lines, foundations, drag lines, power turbines and studs on cranes
and tractors. In many applications, achieving the proper fastener
loading (tension) and maintaining this loading once the system is
placed in service can be problematic. Monitoring the load on a
fastener during installation and service can be equally
problematic.
As a fastener is continually tightened, the load increases until
the fastener ultimately yields, breaks, or its integrity is
otherwise compromised. Thus, overtightening a fastener can lead to
catastrophic failures. Conversely, fasteners typically experience
some loss of tension in service due to, for example, a variety of
in-service occurrences including: relaxation (thread embodiment),
vibration loosening, compressive deformation in the joint or
flange, temperature expansion or contraction, etc. Loss of tension
from these occurrences can cause misalignment or premature wear in
a bolted assembly, leakage (in applications where the fastener is
used for sealing), or catastrophic joint failure due to excessively
high loads on other members of the assembly.
In certain applications, knowledge of a fastener load, upon
installation and over time, is desirable for avoiding the
potentially dangerous consequences of a compromised or loosened
fastener, such as slippage, wear, leakage and/or possible failure.
In other applications, for example when working with a group of
bolts around a flange of a sealed assembly, it is important to
evenly tighten the group of bolts. By uniformly tightening a group
of bolts or studs to an appropriate load, and maintaining this load
over time, potential failures are less likely to be
experienced.
Determining the tensile load of conventional fastener often entails
cumbersome methods to check the tightness of each bolt, such as
loosening and re-tighten all of the fasteners regardless of whether
such re-tightening is needed. The retorquing (i.e. tightening) of a
fastener, however, induces wear and strain in the fastener system.
Additionally, corrosion, friction, variations in nut condition, and
the like can cause variations in torque values and introduce error
into tensile load measurements.
One earlier proposed load indicating fastener, which is the subject
of U.S. Pat. No. 5,668,323 issued Sep. 16, 1997 to Cory S. Waxman
and incorporated herein by reference, includes a single pivot lever
positioned within a bore in the fastener head with the actuator end
of the pivot lever in contact with a reference post or datum rod
seated or formed in the end of the bore and an indicator end of the
pivot lever being visible at the head of the fastener.
Other proposed methods often require costly tools or readers or
special training. For example, electronic or ultrasonic methods for
determining tensile loads require experienced operators, expensive
equipment, clean surfaces and records of pre-installation test
values for each bolt or stud. In addition, such systems may be
adversely affected by shock and other extreme conditions.
Accordingly, improvements are sought in the monitoring of loading
in fasteners.
SUMMARY OF THE INVENTION
The details of one or more embodiments of the invention are set
forth in the accompanying drawings and the description below. Other
features, objects, and advantages of the invention will be apparent
from the description and drawings, and from the claims.
One aspect of the invention features, in combination, a fastener
and load indicator for measuring an axial tensile load on the
fastener. The combination includes a fastener including a head
defining a reference surface and a load indicator interface, and a
shank defining, with the head, a central bore. A datum rod is
anchored at a first end within the central bore and extends along
the central bore to a second free end positioned adjacent the
reference surface of the fastener head. A load indicator housing
defines a fastener interface configured to releasably couple the
load indicator to the load indicator interface on the head of the
fastener. A datum probe extends from the housing and is configured
to be displaced by the datum rod as the load indicator is coupled
to the fastener via the fastener interface. A first lever having
first and second ends and being pivotally coupled to the load
indicator housing and moveable in response to displacement of the
datum probe. A load display retained by the housing is responsive
to movement of the lever to indicate the loading of the fastener as
a function of the displacement of the datum rod, datum probe and
first lever.
In some implementations, a second lever is pivotally connected
within the housing and cooperates with the first lever such that
the load display is responsive to combined movement of the first
and second levers.
In some cases, an end of the second lever is a pointer movable
along a visual scale.
In some implementations, a spring biases the pointer towards one
end of the visual scale.
In some implementations, the load display includes a pointer
movable along a visual scale.
In some implementations, a multi-faceted lens in the housing for
configured to allow viewing of the load display from multiple
substantially orthogonal views. In some cases, the visual scale is
multifaceted or inclined.
In some implementations, the load display is at least one of an
electrical signal, an audible signal and a light signal.
In some implementations, the interfaces couple the indicator to the
fastener via at least one of a snap fit, interference fit, threaded
fit, and magnetic attraction.
In some implementations, the interfaces are configured to align the
datum probe with the free end of the datum rod.
In some cases, a first end of the first lever serves as the datum
probe.
In some cases, second end of the first lever serves as a moveable
pointer.
Another aspect of the invention features a load indicator removably
couplable to a fastener for instantaneous load measurement. The
indicator includes a housing defining a fastener interface
configured to removably couple the housing to a fastener. A
moveable datum probe extending from the housing, the fastener
interface configured to align the datum probe with a datum rod of a
fastener. A first lever is pivotally mounted within the housing and
is moveable in response to displacement of the datum probe. A load
display is configured to indicate a degree of loading of a fastener
as a function of displacement of the datum probe.
In some implementations, the load display includes a visual scale
and a pointer associated with the first lever.
In some implementations, a first end of the lever is the pointer
and a second end of the lever is the datum probe.
In some implementations, the first lever is configured to produce a
first amplified response to movement of the datum probe.
In some implementations, a second lever is associated with the
first lever to produce a second amplified response to movement of
the datum probe.
In some implementations, a spring biases the first lever towards
one end of the visual scale.
In some implementations, the fastener interface is configured to
attach to a complimentary feature on the fastener by at least one
of a snap-fit, interference fit, threaded connection and magnetic
attraction.
In some implementations, the indicator is further configured to
maintain a measured load value on the load display after removal of
the indicator from a fastener.
In some implementations, the load display includes one of an
audible signal generator and a light generator.
One aspect of the invention features a fastener or bolt configured
with a load gauge and a load indicator or gauge reader configured
with a probe responsive to displacement of the load gauge. The bolt
and load indicator are separably or removably coupled during load
readings via complementary indexing interfaces on the bolt and load
indicator.
In some implementations, the load indicator includes a housing
defining a bolt indexing interface and a datum probe extending from
the housing adjacent the bolt indexing interface. The datum probe
is moveable to cause a pointer to move along a visual scale visible
on or through the housing. In some cases the pointer is visible
through a multi-faceted viewer window in the housing.
In some cases the datum probe acts on a series of levers to move
the pointer along the scale. In some cases, the datum probe is a
first end of a first lever and the pointer is a second end of a
second lever, the first and second levers moveable about pivots
with a second end of the first lever cooperating with a first end
of the second lever.
In some cases the datum probe and pointer are opposite ends of a
lever.
In some implementations, the fastener or bolt includes a head and a
shank and central bore defined in the head and shank. A datum rod
is anchored within the central bore in the fastener. The fastener
head defines a reference surface and a load indicator indexing
interface. A free end of the datum rod moves relative to a
reference surface on the fastener head upon loading and elongation
of the fastener. In some cases, a portion of the reference surface
also serves as the load indicator indexing surface. The load
indicator indexing interface on the fastener head and the bolt
indexing interface on the load indicator provides for alignment
and/or temporary mounting of the load indicator atop the
fastener.
As the load indicator is pressed onto the bolt head, until the bolt
indexing interface engages the load indicator indexing interface,
the datum probe of the load indicator is progressively pushed into
the load indicator housing. A gap defined between the free end of
the datum rod and the reference surface is translated into a
measurement of fastener loading via the corresponding movement of
the datum probe, levers and pointer. Thus, the pointer moves along
the visual scale of the load indicator in proportion to the
displacement of the datum probe, which corresponds to the gap
produced between the reference surface and datum rod as a result of
fastener loading.
In some implementations, the datum probe is a ball bearing
displaceable within in a journal and contacting the first
lever.
In some implementations, the load indicator housing includes a
multifaceted lens over the visual scale and pointer, to permit
reading of loading values at both a load indicator end and load
indicator side or from a combined angle. In some cases, the visual
scale includes multiple scales, each separately viewable through
different facets of a load indicator lens in a housing window, or
through separate load indicator housing windows.
In some cases, movement of the datum probe is translated
electronically into a visual indication of fastener loading, e.g.,
via an LCD display.
In some cases, the gap between the datum rod and reference surface
can be additionally or alternatively measured using sonic, optical,
or resistance measurements or other non-contact gap measuring
techniques.
In some implementations, the indexing interfaces of the fastener
and load indicator include cooperative releasably engageable
features. In some cases, the interfaces together include a snap fit
coupling. In some cases, the interfaces together include an
interference fit coupling. In some cases, the interfaces together
include a threaded coupling. In some cases, the interfaces together
include a seated coupling. In some cases, the interfaces together
include a quick connect coupling like those found on air tools. In
some implementations, the load indicator indexing interface of the
fastener includes a recess and the fastener indexing interface of
the load indicator includes a projection or shoulder. Any number or
combination of couplings can be used to align and removably secure
the load indicator on the fastener.
In some implementations, the load indicator includes first and
second cooperating levers, each having first and second ends. The
first free end of the first lever serves as the datum probe and the
second free end of the second lever serves as the pointer. The
levers are pivotally retained on pivot pins within the load
indicator housing. A spring or other biasing device serves to bias
one or more of the levers in a particular direction. For example,
in some cases, a spring biases the cooperating levers such that the
pointer rests adjacent the 100% portion of the visual scale. As the
load indicator is mounted on the fastener, the datum probe contacts
the datum rod and moves the pointer down the visual scale to the
appropriate percentile load indicator.
In some cases grease is provided around the datum rod within the
central bore. In some cases, a removable cap is provided over the
datum rod and central bore when the load indicator is not attached.
For example, the cap can be retained on the fastener head via a
coupling similar to that used to retain the load indicator.
In some implementations, the load indicator includes a lock
configured to maintain the pointer in a fixed position along the
visual scale for reading after removal of the load indicator from
the fastener. In some cases, a second moveable indicator
accompanies the pointer along the visual scale in a first direction
but remains subsequently fixed along the scale to provide an
indication of the reading obtained prior to separation of the load
indicator. The second indicator can then be reset adjacent the
pointer for a subsequent reading.
In some implementations, the load indicator can be coupled to the
fastener independent of a particular rotational orientation, i.e.,
the interfaces together provide for a wide range of orientations.
In other implementations, the indexing interfaces require more
precise positioning of the load indicator on the fastener head. For
example, a series of complementary projections and detents may
allow for only a finite number of discrete orientations.
In some cases, the load indicator is provided with seals around any
housing openings to prevent intrusion of moistures.
In some cases, the use of multiple levers provides for amplified
pointer response while allowing the load indicator housing to be of
a compact construction. For example, the load indicator housing can
be constructed to be generally not substantially larger in diameter
than the fastener head or even than the central bore of the
fastener. Use of multiple levers provides amplified lever end
responses within an overall narrower range of movement than would a
single lever. In some applications with large industrial fasteners,
the load indicator housing is significantly smaller in diameter
than the fastener head.
In some implementations, the load indicator is configured to be
further connected to a power tightening tool to facilitate
automatic shut-off of the tool upon reaching a certain loading, as
indicated by the load indicator. For example, the load indicator
can provide an electrical signal corresponding to the movement of
the datum probe and the tool can be configured to shut-off upon
detection of a predetermined electrical signal value.
In some cases, the load indicator is positioned within a driver on
the tool such that the load indicator and driver are simultaneously
pressed onto the fastener.
In some implementations, a light source is provided adjacent the
visual scale and pointer to allow for low light readings. In some
cases, the light source is an LED powered by a battery. In some
cases, the light source is a phosphorescent coating on at least one
of the pointer and the visual scale.
In some implementations, the load indicator includes multiple
different indexing interfaces for coupling to multiple different
sized fasteners. In some cases, one size of load indicator indexing
interface is used on many different sizes of fasteners to allow use
of one load indicator on a wide range of fastener sizes.
In some implementations, the load indicator includes an audible
signal or light generator. The audible signal or light generator
can be set to activate when a detected loading is within a
predetermined range. Alternatively, it can activate when a detected
loading falls outside an acceptable range, for example, when the
fastener is overloaded or insufficiently loaded.
In some implementations, the load indicator includes a magnet to
help maintain the load indicator in indexed engagement with the
fastener head. In some case, the magnet forms part of the fastener
indexing interface.
In some implementations, the load indicator can be more permanently
coupled to a fastener to provide ongoing loading measurements. For
example, the load indicator can be snap fit or interference fit
onto a fastener head for periodic readings or can be threaded onto
the fastener head to provide ongoing measurements. Thus, the load
indicator can be removably, semi-permanently, or effectively
permanently attached to the fastener to provide a desired frequency
of readings.
In some cases, the load indicator housing is machined from aluminum
or steel. In other cases, the load indicator housing is molded from
plastic. In some cases the levers are stamped from steel sheets and
secured within the housing via steel pivot pins. A spring is
connected between one end of a lever and the housing to bias the
pointer towards a position on the visual scale.
In some cases, the visual scale is provided on an incline to permit
viewing from multiple angles. In other cases, the visual scale is
provided along adjacent angled surfaces to permit viewing from
multiple angles.
In some cases the indicator includes a sensor for sensing said
displacement of the datum probe and translating the displacement
into a readable signal. In some cases, the sensors one of a
displacement transducer and a pressure transducer.
Multiple levers within the load indicator may cooperate to indicate
the load on the fastener by amplification of the elongation
experienced by the fastener. A multi-lever design may provide a
visible range of pointer movement even with a significantly reduced
indicator diameter and a reduced indicator depth.
Aspects of the invention provide an innovative method and apparatus
for visually determining tensile loading during tightening and
throughout the life of a fastener. In accordance with one aspect of
the invention, a first lever is connected at a lower internal pivot
point within an indicator and a second lever is connected at an
upper pivot point of the indicator. The lower end of the first
lever rests upon a datum rod anchored within a fastener, while the
upper end of the second lever serves as a pointer adjacent a visual
scale.
A lower end of the datum rod is anchored within a bore in the
fastener while the upper free end of the datum rod terminates even
with or a fixed distance from a top surface of the fastener head.
As the fastener is tightened, the fastener is elongated causing the
free end of the datum rod to be drawn or displaced further into the
internal fore of the fastener. The datum probe is displaced as a
function of displacement of the datum rod free end, which causes
the pointer end of the second lever to move relative to a visual
scale. Conversely, loss of fastener tension, the datum rod causes
the levers to return toward their original positions.
In accordance with further aspects of the invention, the load
indicator may be incorporated into the fastener itself. For
example, a cartridge carrying the two levers may be assembled and
calibrated within the fastener using multiple fasteners around the
perimeter of the cartridge or, alternatively, using threads formed
on the perimeter of the cartridge. Various embodiments may include
a seal between the cartridge and fastener to protect the load
indicator from water, chemicals, dirt, and other environmental
conditions. To periodically verify proper calibration, the device
may be partially disengaged and slowly returned to the operating
position to verify proper movement of the indicator.
Use of two levers to shift part of the amplified response to the
second lever reduces the range of movement of the first lever and
the degree of clearance required for the first lever. For
in-fastener embodiments, this significantly reduces the dimensions
of the section of the fastener bore required to accommodate the
amplified lever response. Additional advantages afforded by the
present invention include increased sensitivity of the load
indicator, a reduction in the overall length of load indicator and
in the depth of the bore.
BRIEF DESCRIPTION OF THE DRAWINGS
Like reference symbols in the various drawings indicate like
elements.
FIG. 1a is an prior art fastener without an applied load;
FIG. 1b is an prior art fastener with an applied load;
FIG. 2 is a schematic diagram of a cut-away view of a bore of a
fastener housing a single-lever in-fastener prior art load
indicating assembly;
FIG. 3 is a schematic diagram of a cut-away view of a bore of a
loaded fastener housing a dual-lever in-fastener load indicating
assembly according to one embodiment;
FIG. 4 is a schematic diagram of a cut-away view of the fastener
bore and load indicating assembly of FIG. 3 without a load;
FIG. 5 is a top view of an load indicator visual scale and
housing;
FIG. 6A is a schematic diagram of a cut-away view of a fastener
providing in-fastener recessed cartridge mounting in accordance
with one embodiment;
FIG. 6B is a schematic diagram of a cut-away view of an in-fastener
flush-mounted cartridge in accordance with another embodiment;
FIG. 7 is a schematic elevation view of an fastener configured for
use with a load indicator according to one implementation;
FIG. 8 is a perspective view of a load indicator for use with the
fastener of FIG. 7 according to one implementation;
FIG. 9 is a sectional view of the load indicator of FIG. 8 along
line A-A; and
FIG. 10 is a side view of the load indicator of FIG. 8 coupled to
the fastener of FIG. 7
DETAILED DESCRIPTION
The following description is of example implementations of the
invention only, and is not intended to limit the scope,
applicability or configuration of the invention. As will become
apparent, various changes may be made in the function and
arrangement of the elements described in these implementations
without departing from the scope of the invention as set forth
herein.
In accordance with various aspects of the invention, a load
indicator includes a housing or "cartridge" housing or connecting
various indicator elements. The housing or cartridge may be
temporarily mounted to the head of a fastener or may be permanently
mounted within a fastener bore to measure the tensile load of the
fastener. The cartridge includes first and second moveable members
or "levers" that interact to provide an amplified response to the
elongation of the fastener to provide a visual indication along a
visual scale.
While described here in the example context of a bolt, it should be
appreciated that a load indicator may be used with any fastener,
for example, studs, pins, dowels, jack bolts, thread stock, and/or
the like may incorporate aspects of the present invention. Thus, a
fastener, as used herein, means any securing device or structure
capable of elongation in response to an applied force.
The term "lever" as used herein, refers to any rigid or
substantially rigid member having a portion configured to be
moveable relative to a reference point or "pivot" in response to
movement of another portion of the lever. Thus, suitable levers may
be of any shape or size and may be configured and associated with a
pivot in any manner to achieve a desired lever movement.
Similarly, "pivot" as used herein, generally may be construed to
mean any fulcrum or reference by which actuation of a first portion
of a lever causes movement of an opposing second portion of the
lever. For example, the pivot may be a pin positioned to obtain a
specific amplification ratio of the movement of the second lever
portion in response to movement of the first lever portion.
Similarly, the lever lengths and pivot points of the levers may be
selected to achieve a combined amplification ratio.
In general, in accordance with various aspects of the present
invention, elongation of a fastener causes multiple interoperable
levers to display an indication of the tensile load on a visual
scale. The indicator may be used to establish the proper initial
loading of a fastener or to monitor the subsequent loading of the
fastener. That being said, implementations are described herein in
the context of torquing or tightening a fastener to the proper
loading.
In accordance with various embodiments, one or more of the levers
may be biased to return one or more of the levers to a default
position. For example, in various embodiments, the pointer end of
the second lever is biased toward the maximum load portion of the
visual scale. In the context of an in-fastener indicator, the
cartridge is inserted into a central bore of the fastener until
contact with a datum within the bore moves the levers and pointer
to the no load portion of the visual scale. Thus, subsequent
elongation of the bolt would distance the reference from the pivot
of the first lever returning the indicator end of the second lever
proportionately towards the maximum load portion of the visual
scale.
In the context of a removable load indicator, the load indicator
housing/cartridge is temporarily mounted to the head of the
fastener by aligning or indexing a fastener interface on the
indicator with an indicator interface on the fastener. As the
indicator is mounted to the fastener, a datum probe extending from
the load indicator contacts a datum rod anchored within a bore in
the fastener causing the pointer at the end of the second lever to
move proportionately along a visual scale. The indicator may be
snap-fitted, interference-fitted, threaded onto, magnetically
attached or otherwise accurately positioned on the fastener to
ensure accurate readings.
With reference now to FIGS. 1a and 1b, conventional fasteners 5 are
shown in an unloaded state and in a loaded state. As appreciated by
those skilled in the art, a force F applied to fastener 2 causes
fastener elongation that is proportional to the force (F) applied.
Elongation of fastener 2 adheres to Hooke's law, which dictates
that elongation is directly proportional to the load applied to
fastener 2. For example, in FIG. 1a, an initial distance 1.sub.0 is
defined between Point A adjacent the bolt head and Point B located
a predetermined distance from Point A on the shank. With reference
to FIG. 1b, as a force F is applied, fastener 2 is elongated such
that the distance between Points A and B (as shown in FIG. 1b) is
greater than 1.sub.0, namely, as depicted, the distance 1 between
Points A and B. As those skilled in the art will appreciate,
1-1.sub.0=.DELTA..1 and .DELTA..1 is proportional to F, where F is
the force which is applied to fastener 2.
As will be appreciated, .DELTA..1, will vary depending upon the
specific section of fastener 2 that is analyzed. For example, the
elongation in the upper portion of the fastener will tend to be
different than that in the lower i.e. threaded portion of the
fastener. However, within a given region, the percent elongation is
substantially constant over that region. As will be described in
greater detail herein below, the percent elongation over the upper
region of the fastener, such as shown in FIGS. 1a and 1b, is
utilized in determining the load that is applied to the fastener.
The indicator provides a visual indication of clamp load status
during tightening and throughout the life of fastener 2.
With reference to FIG. 2, a schematic diagram shows a cut-away view
of an in-fastener single lever load indicator 1 within an elongated
internal bore 4 of a fastener, including bore sections 4a, 4b, and
4c extending from the head of the fastener to a lower internal
point. Bore section 4a extends into the shank or yieldable portion
of the fastener and is configured to receive a reference datum rod
6 configured to act upon a single elongated lever 8 disposed in
bore section 4b. Lever 8 is moveable within bore 4 about a pivot 10
in response to movement of datum rod 6 during elongation of the
fastener. The dashed lines indicate the resting position 5 of lever
8 prior to elongation of the fastener and the corresponding solid
lines indicate the elongation position 7 of lever 8. As a first end
12 of lever 8 moves in contact with datum rod 6 a second end 14 of
lever 8 produces an amplified response, moving second end 14
between position 5 and position 7. Section 4c is configured to
accommodate the amplified range of movement of second end 14. Thus,
a smaller, less visible movement of datum rod 6 within bore 4 is
converted into a larger, more visible movement at second end 14 of
lever 8.
With the single lever configuration shown in FIG. 2, the depth and
diameter of bore section 4c is determined by the desired amplified
range of movement of second end 14 and the length of lever 8. For
example, for the range of movement of second end 14 to travel a
full half inch visual scale, the diameter of section 4c must be
substantially equal to one half inch. The depth of section 4c, in
turn, must be sufficient to provide clearance for movement of the
remaining length of lever 8. Single lever indicators have proven
very reliable and effective but have typically been limited to use
in fasteners having larger shanks or thicker heads due to the
required depth of bore section 4c. Thus, use of multiple levers
provides for a significantly shallower bore section 4c to enable
use of load indicator 1 in fasteners having smaller diameter shanks
and smaller heads.
With reference to FIG. 3, a cut-away view is shown of a load
indicator 1 having a first lever 8 within bore section 4b and a
second lever 16 disposed within bore section 4c. First end 12 of
lever 8 engages datum rod 6 disposed in bore section 4a causing
lever 8 to respond to movement of datum rod 6 during elongation of
the fastener. Datum rod 6 may be integral to the fastener or may be
a separate component inserted into bore section 4.
A datum rod 6 comprises a post 7 configured to extend a
predetermined distance into section 4a in the shank of the
fastener. Different lengths of post 7 may be used to enable use of
a standard size of load indicator 1 with various lengths of
fasteners having various lengths of bore 4. Datum rod 6 further
includes an annular rim 9 about the top of post 7. Pivot 10 and any
portion of lever 8 may extend into the opening in the center of
annular rim 9. Annular rim 9 serves to contact first end 12 of
lever 8 independent of the orientation of load indicator 1 within
bore 4. It is understood that datum rod 6 may include any other
suitable feature for engaging lever 8 and may be configured for a
particular orientation of load indicator 1 within bore 4. Datum rod
6 may anchored at its lower end in section 4a and substantially
free along the length of post 7 to convey elongation of bore 4 to
load indicator 1.
With continued reference to FIG. 3, a second lever 16 is disposed
within bore 4 and is moveable about second pivot 18. A first end 20
of second lever 16 is responsive to movement of second end 14 of
lever 8 causing corresponding movement of a second end 22 of second
lever 16. First end 20 may be configured to engage lever 8 in both
directions. Alternatively, second lever 16 may be biased in one
direction and moveable in a second direction in response to
movement of lever 8.
Second lever 16 may be sized and configured to provide any desired
degree of response to movement of lever 1. For example, second
pivot 18 may be positioned at the midpoint of second lever 16 or
may be shifted towards one end to further amplify the response of
second lever 16. For example, both levers 8 and 16 may produce
amplified responses, with the sum response being significantly
greater than that provided by a single lever of comparable length.
Second lever 16 is depicted with second pivot 18 positioned
adjacent first end 20 of second lever 16 to provide an amplified
response at second end 22 of second lever 16. Bore section 4c is
sized to accommodate the amplified response movement of second
lever 16.
Comparison of FIGS. 2 and 3 demonstrates advantage provided by
aspects of the present invention with in-fastener mounting
regarding the depth of bore section 4c. By limiting the range of
movement of lever 8 to the smaller diameter of bore section 4b and
shifting the broader amplified response to second lever 16, the
degree of clearance required for lever 8 is significantly reduced
and the depth of section 4c is likewise significantly reduced.
Additional advantages afforded by aspects of the present invention
include increased sensitivity of load indicator 1, a reduction in
the overall length of load indicator 1 and in the depth of bore 4.
Further advantages included increased manufacturing efficiency,
less loss of fastener material to bore 4, and compatibility with
smaller or more conventional fasteners. A multi-lever configuration
provides similar advantages in separable indicators. For example,
the indicator housing or cartridge may be made more compact for use
in tighter areas or with smaller fasteners while allowing for use
of wrenches or other tools to tighten the fastener.
With reference to FIG. 4, a schematic diagram of a cut-away view of
the load indicator of FIG. 3 is shown with levers 8 and 16 in a
second position corresponding to maximum elongation of the fastener
as well as to the default position of levers 8 and 16 prior to
insertion into bore 4. During installation and calibration of load
indicator 1 in bore 4 of a fastener, datum rod 6 is first installed
in bore section 4a and load indicator 1 is then press-fitted or
threaded into bore 4 or is otherwise secured to the fastener.
Additional methods of attaching load indicator 1 to a fastener are
described with reference to FIGS. 5-6.
Load indicator 1 is advanced within bore 4 until first end 12 of
lever 8 contacts datum rod 6. Load indicator 1 is further advanced
until the second end 22 of second lever 16 indicates zero load on a
visual scale associated with second lever 16. It is understood that
any number of load indicator components may be suitably
independently or jointly installed and adjusted to achieve
calibration of load indicator 1. As datum rod 6 moves due to
elongation of the fastener, second end 22 of second lever 16
travels along the visual scale to indicate the corresponding
elongation or loading conditions.
Calibration of load indicator 1 may be performed by loading an
associated fastener in a hydraulic testing fixture to apply a
predetermined load while monitoring the response of load indicator
1. Levers 8 and 16 may be replaced or modified as needed to obtain
proper calibration of load indicator 1. For example, lever 8 may be
replaced with a lever having a slightly different amplification
ratio to achieve a desired amplified response. Once load indicator
1 exhibits the desired amplified response, it may be locked within
bore 4 to maintain proper calibration.
With reference to FIG. 5A, second end 22 of second lever 16 is
moveable along a visual scale 26 within a bezel 28. Visual scale 26
may be viewed from top of the fastener through a protective
transparent lens secured within bezel 28. Visual scale 26 includes
percentage markings indicating a range of proof loads. Any suitable
indication may be used with visual scale 26, including percentages,
fractions, letters, numbers, colors, and the like. A "0%" marking
indicates some minimum load. The location of the "100%" designation
corresponds to a predetermined maximum acceptable load.
Load indicator 1 may be calibrated to about "0%," indicating that
no clamp load forces are present when installed in an unloaded
fastener. Calibration may be suitably accomplished by varying the
position of load indicator 1 within the fastener or the
configuration of any of the components within load indicator 1.
Incremental markings on visual scale 26 suitably allow an
indication of intermediate fastener loads. Alternatively, a
separable load indicator 1 may be calibrated during temporary
mounting on a test fastener.
As previously discussed, upon tightening of a fastener 2 associated
with load indicator 1, fastener 2 experiences tensile loading and
elongates according to Hooke's Law. Elongation of fastener 2
results in movement of datum rod 6 causing the amplified response
of levers 8 and 16 thereby moving second end 22 towards the "100%"
designation on visual scale 26. Upon loosening of fastener 2,
fastener 2 experiences a reduction in tensile loading and shortens
in length. The shortening of fastener 2 increases the pressure
against lever 8 moving second end 22 towards the "0%" designation
on visual scale 26.
In an alternative embodiment, load indicator 1 may include or be
attached to an electronic circuit or other mechanism for initiating
auto shut-off of a pneumatic tightening tool or other powered tool
to prevent over-tightening. Load indicator 1 can also be attached
electronically to a remote reader for automated monitoring of the
clamp load status of a large number of fasteners 2.
Bezel 28 may further include a series of fastener openings 32 and
34. Openings 32 and 34 may be threaded to retain fasteners therein
or may simply permit installation of a fastener to be threaded into
the head of fastener 2 or the end of an indicator housing. For
example, openings 32 permit installation of fasteners configured to
secure bezel 28 to fastener 2 using threaded holes in the head of
fastener 2. Openings 34 are threaded and retain set screws or
locking fasteners for locking bezel 28 into position with respect
to fastener 2 or other indicator housing. For example, fasteners in
openings 32 may be tightened until load indicator 1 provides a zero
load reading and may then be locked in this calibrated position by
tightening fasteners in openings 34, thereby locking bezel 28 in
the calibrated position.
With reference now to FIGS. 6A-6B, a schematic diagram of a
cut-away view of the load indicator 1 of FIG. 5 is shown installed
within fastener 2. In one implementation, load indicator 1 includes
cartridge 36 configured for insertion into bore 4. Cartridge 36
retains pivots 10 and 18 securing levers 8 and 16 within bore 4.
Cartridge 36 may further retain a spring for biasing one of levers
8 or 16 in a default position. Association of levers 8 and 16 and
pivots 10 and 18 with cartridge 36 facilitates easy installation
and removal of load indicator 1 from bore 4. Cartridge 36 is
connected at its upper end to bezel 28.
Bezel 28 may be mounted in a recess in the head of fastener 2 as
shown in FIG. 6A or on top of the head of fastener 2 as shown in
FIG. 6B. In certain applications involving limited space
requirements or high-impact conditions it may be advantageous for
bezel 28 to be located flush with or below the top surface of the
head of fastener 2. Alternatively, as described below, bezel 28 may
be attached to an indicator housing to secure a bi-directional
viewing window.
Load indicator 1 may further include a housing seal 30 and wave
washer 44 between bezel 28 and fastener 2. Housing seal 30 serves
to exclude water, dirt, and other contaminants from bore 4 and load
indicator 1. Housing seal 30 may be omitted, for example, where
load indicator is sealingly press-fitted into bore 4 or otherwise
sealed within an indicator housing. Wave washer 44 serves to
maintain resistance against the fasteners connecting bezel 28 to
fastener 2. Bezel 28 may further retain a transparent lens 40 and
lens seal 42. Lens 40 need not be flat, but may be concave, convex,
curved, angled or otherwise shaped to provide viewing of visual
scale 26. In various alternative embodiments, bezel 28, cartridge
36, or other components of load indicator 1 may serves to attach
load indicator 1 to fastener 2. For example, bezel 28 or cartridge
36 may be press fitted into bore 4. Alternatively, cartridge 36 may
be an enclosed housing as described below that is temporarily
attached to fastener 2 to obtain a load measurement.
With reference now to FIG. 7, a fastener 2 is configured for use
with a separable tensile load indicator shown in FIGS. 8-9.
Fastener 2 defines a central bore 4 extending from the head 3 of
fastener 2 into the shank of the fastener. Datum rod 6 is anchored
at a lower end 6a within bore 4. Head 3 of fastener 2 further
defines a load indicator interface 5 for use as a reference surface
and/or for use in aligning and/or temporarily mounting a load
indicator on fastener 2. Top reference surface 5a of load indicator
interface 5 and top reference surface 6b of datum rod 6 are
coplanar when fastener 2 is in a non-loaded state. As fastener 2 is
tightened, bore 4 is elongated drawing datum rod top surface 6b
downward away from top surface 5a of load indicator interface 5. In
other implementations the datum rod and reference surface are not
necessarily coplanar and another predetermined unloaded relative
positioning of the free end of the datum rod and the reference
surface can be used.
With reference now to FIG. 8, a separable tensile load indicator 80
is configured to be detachably mountable to fastener 2 of FIG. 7.
Load indicator 80 includes a sealed housing 86. Visual scale 26 is
visible through lens 40 secured by bezel 28 atop housing 86. Load
indicator 80 is mounted atop fastener 2 by a bolt indexing
interface 82 configured to connect to load indicator interface 5 of
fastener 2.
Bolt indexing interface 82 may be configured as a socket, clip, or
other interface suitable to couple with load indicator interface 5.
Interface 82 is shown in FIG. 9 as an annular rim constructed and
arranged to engage load indicator interface 5 on fastener 2. It
should be appreciated that interface 5 and interface 82 may be
constructed and arranged in any manner suitable to properly index
indicator 80 with fastener 2 for accurate readings.
For example, fastener 2 need not include a raised interface 5, but
rather may include a recess or other suitable indexing feature. Any
number of alignment or attachment features may be used to ensure
proper alignment and attachment during use. For example, a key and
slot combination feature may ensure proper alignment, while a snap
fit collar feature may ensure full engagement and attachment prior
to reading of load indicator 80.
FIG. 9 shows a sectional view of the separable tensile load
indicator 80 of FIG. 8 taken along line A-A. Housing 86 houses
first lever 16 moveably mounted at pivot 8 and responsive to
movement of lever 8 attached at pivot 10. In this regard, housing
86 is similar to cartridge 36 described earlier. A spring 84 biases
lever 8 or lever 16 towards one end of visual scale 26. For example
second end 22 of lever 16, which extends over visual scale 26 as a
moveable pointer, may be biased towards the 100% load end of visual
scale 26.
First end 12 of lever 8 serves as a datum probe to contact top
surface 6b of datum rod 6, causing lever 8 and interoperable lever
16 to move second end 22 of lever 16 down visual scale 26 to the
appropriate corresponding load indication. Visual scale 26 may be
positioned on an incline below a multi-faceted lens 40 so as to be
visible both from the top and the side of housing 86. Lens 40 may
be configured to provide magnification of visual scale 26.
Alternatively, first end 12 of lever 8 may rest in a default
retracted position until extended into a reading position by a load
indicator operator. Similarly, first end 12 of lever 8 may be
associated with any number of additional datum probe elements, such
as a ball bearing interposed in a journal between first end 12 and
upper surface 6b during reading.
Thus, load indicator 80 may be used during installation or routine
maintenance of fasteners to measure the tensile load or clamp force
of a fastener. Use of a dual lever embodiment provides for a
reduced indicator diameter and height for use in tight areas, or
for ease of use, transportation, storage and manufacture. The
angled lens 40 and inclined visual scale 26 enable observation of
indicator readings from various angles.
A number of embodiments of the invention have been described.
Nevertheless, it will be understood that various modifications may
be made without departing from the spirit and scope of the
invention. For example, three levers could be used to provide
additional amplified response. For example, both a visual
indication and an electrical signal can be provided in response to
movement of the datum probe. Accordingly, other embodiments are
within the scope of the following claims.
* * * * *